Cylinder and piston and method of producing a working seal therebetween



J. WILLIAMS 2,358,271 STON AND METHOD OF PRODUCING 7 Sept. 12, 1944.

CYLINDER AND PI WORKING SEALS THEREBET-WEEN Filed Feb. 7,

j showing a miniature engine embodying the .presentimprovements; u j

Patented Sept. 12, 1944 CYLINDER AND -PISTON AND METHOD OF PRODUCING AWORKING SEAL THERE- BETWEEN Judson Williams, Philadelphia, Pa.Application February '7, 1942, Serial No. 429,914 2 Claims. (chaos-20This invention relates to an improved cylinder and piston and method ofproducing a working seal therebetween, being more particularly concerned with certain improvements and developments arising out of thepractice of the invention disclosed in my copending'application' filedMay 9, 1941, Serial No. 392,796 and bearing the same title.

Under the disclosure in my copending application above identified, thecylinder is first indented externally to provide one or more internalrings on the cylinder wall, when the piston is used to broach said ringsto form a working seal with the piston. It has been discovered, however,that a working seal may be provided between the piston and cylinderwithout first indenting the cylinder wall.

An object of the presentinvention, therefore, is to provide a workingseal between the piston and cylinder without the use of rings on thepiston and without indenting the cylinder wall to form rings. p

A further object of the invention is to provide a construction whereinthe cylinder wall will ;be formed by the piston with an annular,burnished" area to coact with the piston and provide a working sealtherewith, and wherein said area will be of a width substantially equalto the stroke of the piston so that the workingseal betweenpiston andcylinder will be continuous throughout the stroke of the piston. I

Another object of the invention is to provide a construction wherein thepiston will be em ployed to firstbroach the cylinder wall at the providea distinctly defined, circular shearing edge at the upper end of thepiston so that the piston will adequately serve as a broach for shapingthe cylinder wall to the contour of the piston.

Other and incidental objects of the invention will appearduring thecourse of the following description, and. in the drawing:

Figure 1 is a transverse vertical sectional view parts as are pertinent.

Figure 2 is an'enlarged vertical section showing the cylinder beforebeing broached.

Figure 3 is an enlarged fragmentary section showing the piston nearbottom center and on the up-stroke. 1

Figure 4 is a view similar to Figure 3 but showing the piston further upin the cylinder. Figure 5 is an enlarged fragmentary section showing theburnished sealing area formed by thepis ton. a 7

Referring now more particularly to the drawing, it will be seen that Ihave shown the present improvements in conjunction with a miniaturemotor as used upon miniature aeroplanes, miniature motor boats andminiature automobiles as well as for miniature power units, as saidimlarger size, such as automobile engines, as well as other adaptations,such as the injector pumps of Diesel engines and, accordingly, all suchvariations are to be" considered within the spirit and scope of theinvention.

As the construction and operation of the engine as a whole isunnecessary to an understanding of the present invention, 1 have shownonly such The engine is of twocycle design and includes a cylinder H)and crank case I l.

' on therear end of which is a disk !2 carrying a crank pin [3, andreciprocable'in the cylinder is a piston l4 having a wrist pin l5journaling a connecting rod l6 engaged with the crank pin l3. At theupper endof the cylinder is an appropriate firing chamber H.

The cylinder IE! is preferably of a suitable aluminum alloy as is alsothe piston it. Other suitable materialsmay be employed but it has beenfound important, however; that the piston and cylinder have the samecoeiiioient of expansion. For this reason, the piston should be of thesame 7 aluminum alloy as the cylinder, or other material peripheral oilgrooves l 8. In the present instance,

I have shown a' groove above and a groove below,

As particularly chosen. As will be observed, the piston is without ringsbut maybe provided with one or more the wrist pin I 5.

drawing, the wall of the cylinder ill is initially thicker towardtheupper"endofthe cylinder so j that, internallyythe cylinder is more orless-of I The crank case journals a crank shaft. 7

brought out in-Figure 2 of-the 1 the periphery of the firing, chamber11.

Formed within the cylinder Iii at its upper end is a counterboredwall-surface 19. See Figures 3, 4 and 5 of the drawing. After beingfashioned with a tapered bore, the upper end portion of the cylinder is,as seen in Figures 1, 3, 4 and 5 of the drawing, then preferablymachined internally to define the wall surface l9 which forms Thus, thewall of the firing chamber is straight so that the volume of saidchamber will not be reduced by the original taper of the cylinder bore.If deemed necessary, the counterbored firing chamber may in the finishedengine be slightly larger in diameter than the bore of the cylinder atthe lower limit of said chamber or the chamber may be so formed as to beof the same diameter as the bore of the cylinder after being broached bythe piston, as will be later explained.

At the lower end portion of the cylinder, the bore thereof may, assuggested in Figure 2, be

' more or less uniform to' initially receive the pissembled with any onecylinder without the necessity of matching, as it has been foundextremely difucult, in making pistons and cylinders of miniatureengines, to fashion the parts of exactly uniform size. a r a As comparedwtih the wall of the cylinder 10, the piston I4 is hardened inanypreferred manner so that as the engine is broken in, the piston willeffectively provide a broach for shaping said wall. "he piston is ofsubstantially uniform diameter from end to end and the peripheralsurface thereof is smooth while the piston is machined so that the upperend thereof or, at least, the peripheral margin of the upper end of thepiston is square with said surface; A distinctly defined, circularshearing edge is thus provided at the upper end of the piston forinitially broaching the cylinder wall. 7

It is to be understood that Figures 2, 3, 4 and 5 of the drawing havebeen greatly exaggerated and it is not intended that the showing shallcreis but one way of initially forming the cylinder; If preferred, thelower end portion of the cylinder may be of one uniform internaldiameter to receive the piston [4 with a close working fit, and theupper. end portion of the cylinder of a -slightly smaller initial,internal diameter, the

junction between the two being. gradually merged.

7 As thepiston is to act as a broach while the engine is being brokenin,the lower end porjtion of the bore of the cylinder must, of course,be

- fashioned to a'close working fit with the piston" expensive.

in order that the piston may be initially installed. However, in anyevent, it is intended that the internal contour of the wall of thecylinder will initiallybe such that said wall will be broached by thepiston, as the engine is broken in, for substantially the full length ofthe stroke of the piston.

Assuming now that the piston [4 has been initially installed in thecylinder l0 and the engine is to be broken in, it has been found thatthis may be accomplished by operating the engine under its own power. Asthe piston moves upwardly inthe cylinder, the shearing edge 20 of thepiston will function to broach the wall of the cylinder tothe exactperipheral contour of the piston sothat, after a very short time, thepiston will reciprocate without broaching effect and the engine willoperate freely. The period of time required to break in the engine hasbeen found to be'very short, after which the broaching effect of thepiston on the cylinder wall ceases and said wall is subjected by thepiston only to a burnishing action. t

Figure 3 of the drawing shows the piston I 4 near the beginning of itsupward stroke while Figure 4 shows the piston further up in thecylinder. As will be appreciated, the piston will, as the engine isbroken in, broach the cylinder wall substantially throughout the fullstroke of the piston, after'which the broached band will be burnished bythe piston to provide, as seen in Figure 5, a highly polished, annularsealing area 2| to coact with the piston and provide a working sealtherewith.

It is to be noted that since the cylinder wall is broached by the'piston, the sealing area 2| will exactly conform to the contour of thepiston throughout the periphery thereof so that a working seal betweenpiston and cylinder will be provided throughout the circumference of thepiston. As is well known,-such a circle-seal may not be completelygained by the use of piston rings and, moreover, since in the presentinstance the use of rings on the piston is eliminated, the frictionaldrag of such rings is avoided. Fmthermore, it is to be noted that thesealingsurface 2| will exert no resilient, gripping drag on the pistonor, at least, no appreciable drag in any way comparable to the dragexerted by resilient rings eitheron the piston or on the cylinder wall.This factor has been found of great'gain in a miniature engine while,also, the necessity for lapping the cylinder and piston is avoided.

Experience in the manufacture'of miniature engines hasshown that it isdifiicult to produce such small pistons exactly round and maintainlow-cost production. Also, the'small rings required for such a pistonhave been found to be However,-by utilizing the piston to broach thecylinder wall, the sealing surface 2| will fit the piston even thoughthe piston may be slightly out-of-round while, also, a more effectiveworking seal :will be had between piston and cylinder than if rings wereemployed on the piston. In adapting the invention to Diesel injectorpumps, however, or in other similar adaptations, it may be necessary tofashion the piston exactly round as, for certain of the pumps noted,.thepiston must be rotated as well as reciprocated while, also, thecircle-seal between piston and cylinder must still be maintained.

bination of a cylinder having a'roughly finished V bore the lower endportion of which is of uniform diameter and the upper end portion ofwhich is tapered toward the upper end of the cylinder,

and a piston reciprocal in said cylinder to form a working part of theengine and of uniform diameter to freely fit in the lower end portion ofsaid bore, the piston having an individual rough- 1y finished peripheralcontour untreated to match the lower end portion of the bore of thecylinder t 2. The method of forming a working seal between a cylinderand coacting piston unfinished to match each other which includes thesteps of forming the bore of the cylinder straight at its lower endportion and tapered at its upper end portion toward the upper end of thecylinder,

forming the piston with a roughly finished in-V dividual peripheralcontour to freely fit in the straight portion of said bore, treating thepiston to render the same harder than the material of thecyliridenfinishing the upper end of the piston to define a hardenedperipheral cutting edge, and cutting the tapered portion-0f the bore ofsaid cylinder by said" edge as the engine is broken in to the exactroughly finished peripheral contour of the piston and establishing aclose-fitting working seal between the piston and cylinder.

i JUDSON WILLIAMS.

